The present invention relates to a molecular vacuum pump with a stator having a stator blade package including several rows of stator blades, as well as a rotor having a rotor blade package including several rows of rotor blades. The rows of stator blades and the rows of rotor blades intermesh with each other in functionally assembled state.
With the known molecular vacuum pumps of this type, the stator and rotor, in cross section, form a ring shaped transport chamber, into which the rows of stator and rotor blades project in intermeshing fashion. The pitch angles of the stator blades are inversely oriented vis-a-vis the pitch angles of the rotor blades with regard to their blade row plane.
The rotor of these type of friction vacuum pumps is traditionally designed in one piece, while the stator has a multitude of components. The stator ring package typically includes two semi-annular shape components, each with intermeshing profiles; that alternate with stator blade rings, which are joined to define the stator. With respect to manufacture as well as installation of disassembly, friction vacuum pumps of this type are extremely costly. Additional drawbacks are as follows:
Due to the multitude of components, relatively large gaps result between stator and rotor, which leads to relatively high backstreaming losses;
with small pumps, the handling of the working components becomes particularly problematical during installation;
despite reduction in the size of the components, no noticeable cost reduction can be achieved vis-a-vis larger pumps.
The present invention is based on the object of creating a friction vacuum pump of the initially mentioned kind, which no longer has the described drawbacks.
According to one aspect of the invention, said object is solved in that the blades of one of the two blade packages are equipped with slots, whose arrangement, depth and width are selected in such fashion that stator and rotor can be screwed together and unscrewed from each other. With a molecular vacuum pump of this type it is no longer necessary to produce the stator from a multitude of components.
Stator as well as rotor can respectively be designed in one piece and can thus be produced cost-effectively. The handling of components of this type during installation is significantly less complicated. The gaps between rotor and stator can be drastically reduced, since, due to the reduced number of components. There is significant reduction in the extent of permissible tolerance. This results in smaller backstreaming losses or improved pumping properties. The tooling costs for the production of the stator are significantly lower, so that more flexible stator designs are no longer associated with particularly high increases in cost.
It is of particular benefit that blades may be provided on the interior side of the rotor, for example of a bell-shaped rotor, which correspond to stator blades of an inner stator. In particular, with pumps having co-axially nested vane cylinders, lower construction height can be achieved. In addition, with a blade configuration of this type, the motor and the storage compartment can be evacuated as a safeguard against the utilization of aggressive or reactive gases. Separate blocking gas equipment can be eliminated.
Ultimately, it is of benefit that the blade lengths may be as small as desired. If they have a length, for example, which corresponds to the depth of a threaded known with Holweck-Pump stages, then a new pump surface geometry is created (Englander geometry) which is particularly effective in the field of laminar or viscous flow. For all practical purposes, there is a constant change between rotor and stator thread gear, so that there is substantial reduction in backstreaming compared with the Holweck Technique. Pump surface according to the new pump surface geometry are effective even when the laminar flow changes to turbulent flow, so that significant improvement is achieved with respect to pre-vacuum stability. Another benefit lies in that it is possible to change over, continuously, from the Turbo-Principle to the Englander Geometry, which makes it possible to prevent transfer losses and improve the overall efficiency degree of the pump.
Another reduction in backstreaming losses can be obtained in that stator and rotor can be coupled relative to vibration and that the system comprising stator unit and rotor unit is jointly fastened in the housing by means of vibration elements.